The proposed research will assess the significance of vestibular self-stimulation during infancy for sensorimotor development in normal children. Vestibular self-stimulation (e.g., rocking, head banging, head or body rolling) is a class of behaviors reported to occur in approximately 15-20% of the normal infant population, but despite its prevalence it has not been systematically studied. The first part of this investigation will assess by means of a retrospective questionnaire the incidence in an unselected pediatric clinic population 9 to 60 months of age of vestibular self-stimulatory activity and the circumstances under which it occurs. In the second part of this study the significance of vestibular self-stimulation during infancy for later sensorimotor development will be assessed by means of a retrospective questionnaire on infant self-stimulation administered to the mothers of a group of preschool children whose motor coordination and balance will be measured by the Lincoln-Oseretsky Motor Development Scale. It is hypothesized that children who experienced an unusual amount of vestibular stimulation during infancy will be relatively advanced on measures of motor coordination and balance. The pre-school children will also be assessed for responsivity to strong rhythmic stimulation by music. The third part of this investigation will relate a measure of vestibular functioning (vestibular nystagmus induced by rotation in a chair controlled with respect to angular acceleration and constant velocity) to the presence or absence of vestibular self-stimulation in clinically normal infants 9-12 months of age.